Position identifier management apparatus and method, mobile computer, and position identifier processing method

ABSTRACT

When a first mobile node is moved, it reports binding information including a compatible node identifier (virtual mobile guaranteed general network identifier and a node identifier) and a compatible position identifier (mobile guaranteed real network identifier identified on a network to which the first mobile node is moved, and a node identifier) to a first server which is assigned to the first mobile node. A second mobile node also reports the binding information to a second server. For communicating with the second mobile node to which a second server is assigned, if the destination address of a packet addressed to the second mobile node is designated with a compatible node identifier, the first mobile node acquires the binding information of the second mobile node from the second server. Then, the first mobile node converts the destination address of the packet into the acquired compatible position identifier and sets the compatible position identifier of the first mobile node as the source address of the packet. The first mobile node then transmits the packet.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to mobile computers for performingcommunication while moving between a plurality of interconnectednetworks. The invention also relates to a position identifier managementapparatus and method, and a position identifier processing method forprocessing position identifiers concerning the above-described mobilecomputers.

[0003] 2. Description of the Related Art

[0004] Along with the widespread use of the Internet, which is thelargest worldwide computer network, users have become able to obtainpublicly available information and services by connecting to theInternet, and also, new computer businesses are being developed byproviding information and services to users who make access through theInternet. New technologies for the use of the Internet are also beingdeveloped. Additionally, due to a progress in the implementationtechniques of computers, small and light computers are becoming popular,and it is no longer unusual for the users to carry computers with them.

[0005] In the Internet, each computer possesses an identifier, which isreferred to as an Internet protocol (IP) address”, and based on the IPaddresses, packet switching is performed. However, IP addresses servenot only as identifiers for computers, but also as identifiersrepresenting the positions of computers on a network (hereinaftersometimes referred to as “position identifiers”). Accordingly, when acomputer is moved on a network, it is handled as different computers onthe network before and after being moved, even though they are actuallythe same computer.

[0006] In today's world in which mobile computers have becomewidespread, it is inconvenient if the same computer is handled asdifferent computers every time it is moved. For example, a systemadministrator is unable to conduct authentication based on IP addressesas intended, or the session used while the computer is moved isterminated.

[0007] In order to avoid such problems, the Internet Engineering TaskForce (IETF), which is an IP standardizing organization, has set up amobile IP. The mobile IP is a system in which a mobile computer is ableto use the unique IP address (which is referred to as the “homeaddress”) without depending on where the computer is positioned on anetwork.

[0008] A mobile computer sets this home address as the source address ofan IP packet. A receiver receives the packet and then sends a packet tothe mobile computer by setting the home address as the destinationaddress. With this arrangement, however, the packet will not reach themobile computer which has been moved away from the home address. Thus,according to the mobile IP, a home agent is provided on the networkwhich is compatible with the home address. When a packet is sent to themobile computer which has been moved away from the home address, thehome agent receives the packet for the mobile computer and transfers itto the mobile computer. The mobile computer regularly reports thecurrent position to the home agent.

[0009] According to the above-described control, when the mobilecomputer moves, communication between the mobile computer and a receiveris performed in a path, which is formed in a triangle shape, via thehome agent. This is redundant and lowers the transmission efficiency. Inorder to solve this problem, optimization of the path has been proposedin the mobile IP. In order to optimize the path, the mobile computerreports the current position thereof to the receiver, and the receivertransfers the packet addressed to the home address to the currentposition of the mobile computer, thereby eliminating the redundancy ofthe path.

[0010] However, such a mobile IP presents the following problems.

[0011] The presence of the home agent is essential, and the home agentmust be positioned on the network which is compatible with the homeaddress. This makes it difficult to ensure redundancy of the home agentbecause there is only one home address, and there is only one IP networkwhich is compatible with the home address. In other words, it ispossible to provide a plurality of home agents on one network, but it isimpossible to provide a home agent on another network to improveredundancy. Thus, although redundancy against a failure occurring in thehome agent apparatus can be ensured, redundancy against a failureoccurring in the network on which the home agent is placed cannot beensured.

[0012] The problem of the protocol overhead is also encountered.Basically, for transmitting packets to a mobile node (computer), anencapsulating technique employed on the same layer, which is referred toas the “tunneling technique”, is employed. A header providing techniquefor controlling the path is also employed. In this technique, whentransmitting a packet to a mobile node, not only the home address, butalso routing header information is added to the header, thereby directlytransmitting the packet to the mobile node without via the home agent.According to these techniques, the data amount of protocol header isincreased, and the substantial communication performance is lowered.

[0013] Additionally, in the mobile IP of IP version 6 (IPv6), newoptions have been defined after products manufactured based on thefundamental standards of IPv6 were put on sale. Accordingly, new nodesimplemented based on the new options may not be able to communicate withthe old nodes implemented based on the old basic standards.

[0014] In short, according to the conventional mobile IP technique, theredundancy of the home agent for managing the relationship between thehome address of a mobile computer and the current position thereofcannot be enhanced. Additionally, the protocol overhead is increased,and communication cannot be performed between nodes having basic IPv6standards and new nodes having the mobile IP.

SUMMARY OF THE INVENTION

[0015] Accordingly, in view of the above background, it is an object ofthe present invention to provide a position identifier managementapparatus for relating an identifier for uniquely specifying a mobilecomputer regardless of its position on a network with an identifierrepresenting the current position of the mobile computer on the network,in which the redundancy of the management apparatus is enhanced, theprotocol overhead incurred in communication for supporting the movementof the mobile computer is reduced, and communication between a computerhaving a mobile function and a computer without such a function isachieved, and also to provide a position identifier management methodand a position identifier processing method for use in theabove-described position identifier management apparatus.

[0016] In order to achieve the above object, according to one aspect ofthe present invention, there is provided a position identifiermanagement apparatus for supporting the movement of a mobile computerbetween networks. The position identifier management apparatus includesa storage unit for storing binding information concerning the mobilecomputer managed by the position identifier management apparatus, thebinding information including a compatible node identifier for uniquelyspecifying the mobile computer and a compatible position identifier foruniquely specifying a position of the mobile computer on a network. Aregistration unit registers the binding information in the storage unitin response to a registration request to register the bindinginformation from another apparatus. A transmitting unit transmits thebinding information in response to a query about the binding informationconcerning the mobile computer from another apparatus when the bindinginformation is stored in the storage unit.

[0017] Preferably, the aforementioned position identifier managementapparatus may further includes: a unit for registering bindinginformation contained in the received registration request afterdetecting that a sender of the received registration request is anexternal mobile computer and authenticating the external mobile computeras a valid mobile computer; a unit for sending the registration requestto an external position identifier management apparatus which alsomanages the external mobile computer when the external mobile computeris authenticated as a valid mobile computer; and a unit for registeringthe binding information contained in the received registration requestin the storage unit after detecting that the sender of the receivedregistration request is an external position identifier managementapparatus and authenticating the external position identifier managementapparatus as a valid apparatus.

[0018] Preferably, the above-described transmitting unit may transmitthe binding information containing the compatible node identifier whichis identical to the compatible node identifier contained in the query.

[0019] Preferably, the binding information may include a registered timeand an effective period, and the position identifier managementapparatus may further include a unit for erasing the binding informationwhich has expired.

[0020] Preferably, the compatible node identifier of the mobile computermay include a first virtual network identifier assigned to the mobilecomputer which moves between networks and a node identifier for uniquelyspecifying the mobile computer, and the compatible position identifierof the mobile computer may include a second network identifier which isusable only by mobile computers assigned to a network to which themobile computer is connected and the node identifier.

[0021] Preferably, after completion of the registration in response tothe registration request from the mobile computer, the positionidentifier management apparatus may further include a unit fortransmitting a registration response to the mobile computer.

[0022] According to another aspect of the present invention, there isprovided a mobile computer which moves between networks. The mobilecomputer includes a first storage unit for storing binding informationincluding a compatible node identifier and a compatible positionidentifier, the compatible node identifier including a first virtualnetwork identifier assigned to the mobile computer which moves betweennetworks and a node for uniquely specifying the mobile computer, thecompatible position identifier including a second network identifierwhich is usable only by mobile computers assigned to a network to whichthe mobile computer is connected and the node identifier. A secondstorage unit stores binding information concerning at least one ofexternal mobile computers with which the mobile computer is tocommunicate, the binding information including a compatible nodeidentifier and a compatible position identifier, the compatible nodeidentifier including a first virtual network identifier assigned to theexternal mobile computer which moves between networks and a nodeidentifier of the external mobile computer, the compatible positionidentifier including a second network identifier which is usable only bymobile computers assigned to a network to which the external mobilecomputer is connected and the node identifier of the external mobilecomputer. A determining unit determines whether the binding informationis to be used for a packet transmitting or receiving operation. Aconversion unit performs, when the determining unit determines that thebinding information is to be used, a conversion operation by convertingthe compatible node identifier to the compatible position identifierwhen the packet is to be transmitted and by converting from thecompatible position identifier to the compatible node identifier whenthe packet is to be received.

[0023] Preferably, the above-described determining unit may determinethat the conversion operation is to be performed by the conversion unitwhen a destination address of the packet to be transmitted is designatedwith the compatible node identifier.

[0024] Preferably, when the determining unit determines that theconversion operation is to be performed by the conversion unit in orderto transmit the packet, the conversion unit may acquire the compatibleposition identifier corresponding to the compatible node identifierwhich designates the destination address of the packet to betransmitted, and may then convert the destination address of the packetinto the acquired compatible position identifier, and may set thecompatible position identifier of the mobile computer stored in thefirst storage unit as a source address of the packet.

[0025] Preferably, the determining unit may determine that theconversion operation is to be performed by the conversion unit when asource address and a destination address of the packet to be receivedare designated with the compatible position identifiers.

[0026] Preferably, when the determining unit determines that theconversion operation is to be performed by the conversion unit in orderto receive the packet, the conversion unit may convert the compatibleposition identifier into the compatible node identifier by at leastsubstituting the second network identifier contained in the compatibleposition identifier which designates the source address of the packet bythe first virtual network identifier, and may also verify the integrityof the compatible node identifier which designates the source address ofthe packet.

[0027] Preferably, when the determination unit determines that theconversion operation by the conversion unit is not performed, it may beassumed that each of a source address and a destination address of thepacket is a position identifier for uniquely specifying the position ofthe mobile computer on a network and containing a third networkidentifier which does not support the movement of the mobile computer,and the packet may be transmitted or received by using the sourceaddress and the destination address.

[0028] Preferably, the aforementioned mobile computer may furtherinclude: a movement detection unit for detecting the movement of themobile computer by a change in a third network identifier which does notsupport the movement detected on a network to which the mobile computeris connected; an acquiring unit for acquiring the second networkidentifier when the movement of the mobile computer is detected; agenerating unit for generating new binding information based on theacquired second network identifier; and an updating unit for updatingthe binding information concerning the mobile computer stored in thefirst storage unit by the new binding information generated by thegenerating unit.

[0029] Preferably, the aforementioned mobile computer may furtherinclude: a first specifying unit for specifying a position identifiermanagement apparatus which manages the mobile computer from positionidentifier management apparatuses, disposed on a network, for storingthe binding information which is requested to be registered by mobilecomputers managed by the position identifier management apparatuses andfor responding to a query about the binding information; and aregistration request sending unit for sending the new bindinginformation concerning the mobile computer generated by the generatingunit to the position identifier management apparatus specified by thefirst specifying unit.

[0030] Preferably, the above-described mobile computer may furtherinclude: a second specifying unit for specifying a position identifiermanagement apparatus which manages an external mobile computer withwhich the mobile computer is to communicate, from position identifiermanagement apparatuses, disposed on a network, for storing the bindinginformation which is requested to be registered by mobile computersmanaged by the position identifier management apparatuses, and forresponding to a query about the binding information; a query sendingunit for sending, when the second storage unit does not store effectivebinding information about the external mobile computer, a query aboutthe binding information concerning the external mobile computercontaining the compatible node identifier to the position identifiermanagement apparatus specified by the second specifying unit; a responsereceiving unit for receiving a response to the query from the positionidentifier management apparatus specified the second specifying unit;and a registration unit for registering the binding informationconcerning the external mobile computer contained in the receivedresponse in the second storage unit.

[0031] Preferably, the binding information may include a registered timeand an effective period, and the mobile computer may further include aunit for erasing the binding information which has expired.

[0032] According to still another aspect of the present invention, thereis provided a position identifier management method including the stepsof: storing by a mobile computer latest binding information including acompatible node identifier and a compatible position identifier in astorage unit of the mobile computer when the movement of the mobilecomputer is detected, the compatible node identifier containing a firstvirtual network identifier assigned to the mobile computer which movesbetween networks and a node identifier for uniquely specifying themobile network, the compatible position identifier containing a secondnetwork identifier which is usable only by mobile computers assigned toa network to which the mobile computer is moved and the node identifier;specifying by the mobile computer at least one position identifiermanagement apparatus which manages the mobile computer from positionidentifier management apparatuses, disposed on a network, for storingthe binding information which is requested to be registered from anexternal mobile computer managed by the position identifier managementapparatuses, and for responding to a query about the bindinginformation; sending a registration request to register the latestbinding information about the mobile computer from the mobile computerto one of the specified position identifier management apparatuses;storing the binding information contained in the registration request inthe storage unit of the position identifier management apparatus whichhas received the registration request after the position identifiermanagement apparatus detects that the sender of the registration requestis the mobile computer and authenticates the mobile computer as a validmobile computer; and sending the registration request to an externalposition identifier management apparatus which also manages the mobilecomputer after the mobile computer which has sent the registrationrequest is authenticated as a valid mobile computer.

[0033] Preferably, in the position identifier management method, themobile computer may send a query containing the position node identifierof the mobile computer to a server for storing a relationship betweenthe compatible node identifier and an address of a position identifiermanagement apparatus which manages the mobile computer provided with thecompatible node identifier, and may receive a response to the query fromthe server, thereby specifying the position identifier managementapparatus which manages the mobile computer.

[0034] According to a further aspect of the present invention, there isprovided a position identifier processing method for a mobile computer,including the steps of: storing binding information including acompatible node identifier and a compatible position identifier in astorage unit of the mobile computer, the compatible node identifiercontaining a first virtual network identifier assigned to the mobilecomputer which moves between networks and a node identifier for uniquelyspecifying the mobile computer, the compatible position identifiercontaining a second network identifier which is usable only by mobilecomputers assigned to a network to which the mobile computer isconnected and the node identifier; acquiring, when a destination addressof a packet to be transmitted is designated with the compatible nodeidentifier and when the storage unit does not store the compatible nodeidentifier, the binding information containing the compatible nodeidentifier by making a query to a position identifier managementapparatus which manages the binding information concerning a mobilecomputer provided with the compatible node identifier; and convertingthe compatible node identifier representing the destination address ofthe packet to be transmitted into the acquired compatible positionidentifier, and setting the compatible position identifier of the mobilecomputer stored in the storage unit as the source address of the packet.

[0035] Preferably, in the aforementioned position identifier processingmethod, when an error message indicating that the packet has not reachedis returned after sending the packet having the compatible positionidentifiers as the source address and the destination address, a querymay be made to the position identifier management apparatus whichmanages the binding information concerning the mobile node provided withthe compatible node identifier corresponding to the compatible positionidentifier so as to acquire the latest binding information concerningthe mobile computer provided with the compatible node identifier, andthen, the packet may be re-transmitted.

[0036] According to a yet further aspect of the present invention, thereis provided a position identifier processing method for a mobilecomputer, including the steps of: storing binding information includinga compatible node identifier and a compatible position identifier in astorage unit of the mobile computer, the compatible node identifiercontaining a first virtual network identifier assigned to the mobilecomputer which moves between networks and a node identifier for uniquelyspecifying the mobile computer, the compatible position identifiercontaining a second network identifier which is usable only by mobilecomputers assigned to a network to which the mobile computer isconnected and the node identifier; and converting, when each of a sourceaddress and a destination address of a received packet is designatedwith the compatible position identifier, the compatible positionidentifier into the compatible node identifier by at least substitutingthe second network identifier of the compatible position identifierwhich designates the source address of the packet by the first networkidentifier, and also verifying the integrity of the compatible nodeidentifier which designates the source address of the packet.

[0037] The above-described apparatus may be accomplished by theabove-described method, and vice versa.

[0038] The above-described apparatus and method may be implemented by acomputer-readable recording medium for storing a program which causes acomputer to execute the process corresponding to the present invention(or which causes a computer to function as the process corresponding tothe present invention, or causes a computer to implement the functionscorresponding to the present invention).

[0039] According to the present invention, instead of using the conceptof a home network, which is employed in the conventional mobile IP, theposition identifier management apparatus is provided for identifying arelationship between the compatible node identifier which uniquelyspecifies a mobile computer and a compatible position identifier whichuniquely specifies the position of the mobile computer on a network.Accordingly, binding information concerning a mobile computer to becommunicated can be acquired from the position identifier managementapparatus, and packets can be transmitted and received whileautomatically performing conversion between a compatible node identifierand a compatible position identifier. It is thus possible to enhanceredundancy of the position identifier management apparatus.Additionally, the need for using the encapsulating technique can beeliminated, thereby making it possible to reduce the protocol overheadwhile the communication which supports the movement of the mobilecomputer between networks by using a compatible nodeidentifier/compatible position identifier is performed. A mobilecomputer is able to perform both the communication which does notsupport the movement by using a regular position identifier and thecommunication which supports the movement by using the compatible nodeidentifier/compatible position identifier, thereby enablingcommunication between a computer with a compatible nodeidentifier/compatible position identifier and a computer without acompatible node identifier/compatible position identifier.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 illustrates an example of the configuration of a networkaccording to an embodiment of the present invention;

[0041]FIG. 2 illustrates an example of binding information;

[0042]FIG. 3 illustrates an example of binding information;

[0043]FIG. 4 is a block diagram illustrating an example of a positionidentifier management apparatus shown in FIG. 1;

[0044]FIG. 5 is a block diagram illustrating an example of a positionidentifier processing apparatus loaded in a mobile computer shown inFIG. 1;

[0045]FIG. 6 illustrates the operation performed by the embodiment shownin FIG. 1;

[0046]FIG. 7 is a flow chart illustrating an example of the initialsetting processing when a mobile node is moved;

[0047]FIG. 8 is a flow chart illustrating an example of the packettransmitting processing performed by a mobile node;

[0048]FIG. 9 is a flow chart illustrating an example of the packetreceiving processing performed by a mobile node;

[0049]FIG. 10 illustrates the operation performed by the embodimentshown in FIG. 1;

[0050]FIG. 11 is a flow chart illustrating an example of the processingfor detecting the movement of a mobile node by another mobile node whilecommunication is being performed between the two nodes; and

[0051]FIG. 12 illustrates the operation performed by the embodimentshown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention is described in detail below with referenceto the drawings through illustration of a preferred embodiment.

[0053] In the following embodiment, an IPv6 network is applied to thepresent invention.

[0054]FIG. 1 illustrates an example of the configuration of a networkaccording to an embodiment of the present invention. In FIG. 1, N1through N3 indicate sub-networks, and a network 6, for example, theInternet according to IPv6, connects the sub-networks N1 through N3 toeach other. The number of sub-networks is not restricted to three, andthe sub-networks may be configured in a hierarchical structure. Adescription of router devices and various server devices disposed in thesub-networks is omitted. In the subsequent description, a “node” is acomputer.

[0055] A computer 3 is able to perform two types of communications, suchas a first communication performed according to a position identifier,such as a regular network layer address in IPv6 (IP address)(hereinafter referred to as the “regular position identifier”), whichrepresents the position of a computer on a network and which does notsupport the movement of the computer between networks, and a secondcommunication performed according to a compatible node identifier/acompatible position identifier, which are discussed in detail below. Forexample, in a computer M1 in FIG. 1, G1m1 is a regular positionidentifier, while Oi1 and L1i1 are a compatible node identifier and acompatible position identifier, respectively.

[0056] In a computer which is able to perform the second communication,a certain unique IP address (i.e., compatible node identifier) is neverchanged even if the position identifier is changed by moving betweennetworks. Accordingly, such a computer is hereinafter referred to as a“mobile node”.

[0057] On the other hand, a computer 4 is able to perform the firstcommunication according to the regular position identifier (for example,G3c1 of a computer C1 shown in FIG. 1). However, unlike the computer(mobile node) 3, the computer 4 is not able to perform the secondcommunication according to the compatible node identifier/compatibleposition identifier. Since the computer 4 cannot move between networksby communication, it is hereinafter referred to as a “fixed node”.

[0058] In this embodiment, the second communication (mobilecommunication) is achieved only between mobile nodes, while the firstcommunication (non-mobile communication) is achieved between a mobilenode and a fixed node, between fixed nodes, and between mobile nodes.

[0059] In the first communication, the regular position identifier isused for identifying both the node and the position of the node on thenetwork. Accordingly, the movement of the node is not supported.Conversely, in the second communication, the node is identified by thecompatible node identifier, while the position of the node on thenetwork is identified by the compatible position identifier.Accordingly, the movement of the node is supported. In this embodiment,therefore, a mechanism is provided for solving the problem inherent inthe current compatible position identifier by using the compatible nodeidentifier of the mobile node 3. The relationship between the currentcompatible position identifier and the compatible node identifier isreferred to as “binding”. Information concerning the compatible positionidentifier, the compatible node identifier, and additional informationconcerning the mobile node is hereinafter referred to as “bindinginformation”. In this embodiment, the additional information contains atleast a registered time and an effective period of the binding.

[0060] For supporting the second communication, i.e., the movement ofmobile nodes, a position identifier management apparatus (hereinafterreferred to as the “binding server”) 2 manages and stores the bindinginformation of the mobile nodes 3 which are under the control of thebinding server 2, and provides search services concerning the bindinginformation (in particular, solving the problem of the compatibleposition identifier by using the compatible node identifier). The samemobile node can be managed by a plurality of binding servers 2.

[0061] For implementing the second communication in addition to thefirst communication, a position identifier processing apparatus 31 isadded to an IP processing apparatus of the mobile node 3. That is, theposition identifier processing apparatus 31 is extended from an IPprocessing apparatus, which processes IP packets by using the regularposition identifier provided for a fixed node, by adding a positionidentifier processing function. The basic functions of the positionidentifier processing apparatus 31 are as follows.

[0062] The position identifier processing apparatus 31 determineswhether a current communication is the first communication according tothe regular position identifier or the second communication according tothe compatible position identifier/compatible node identifier.

[0063] If the second communication is being made, the compatible nodeidentifier and the compatible position identifier are converted so thatcompatible node identifier is used on an upper layer, such as anapplication on the node, and the compatible position identifier is usedin performing packet transfer on the network.

[0064] Accordingly, as will be discussed in detail below, the positionidentifier processing apparatus 31 processes the position identifiers,such as managing and storing binding information concerning the mobilenode 3 and a receiver node, and registering the binding information andmaking a query about the binding information to the binding server 2,and converting between the compatible node identifier and the compatibleposition identifier when sending and receiving packets.

[0065] A description is now given of the individual identifiers used inthis embodiment (in particular, relationships and differences among theregular position identifier, the compatible node identifier, and thecompatible position identifier).

[0066] (Lower bits of network layer address)

[0067] An identifier assigned uniquely in the world to each node isreferred to as a “node identifier” (for example, “i1” assigned to nodeM1 in FIG. 1).

[0068] In contrast, an identifier assigned uniquely in the world to eachcommunication interface loaded in a node is referred to as an “interfaceidentifier” (for example, “m1” assigned to node M1 in FIG. 1). Theinterface identifier has, for example, 64 bits.

[0069] The above-described node identifier and the interface identifierare used for lower bits of the network layer address, and eachidentifier has, for example, 64 bits.

[0070] (Upper bits of network layer address)

[0071] A network prefix is referred to as a “network identifier”. Inthis embodiment, the network identifiers include not only a networkidentifier, which forms a regular position identifier, (for example,“G1” assigned to the sub-network N1 in FIG. 1), but also a mobileguaranteed real network identifier (for example, “L1” assigned to thesub-network N1 in FIG. 1) and a mobile guaranteed general networkidentifier (for example, “O”, which is determined for all the mobilenodes). These identifiers are used for upper bits of the network addresslayer, and each identifier has, for example, 64 bits.

[0072] (Identifier having a format of the network layer address)

[0073] In this embodiment, identifiers having a format of the networklayer address include a regular position identifier, a compatibleposition identifier, and a compatible node identifier. Such anidentifier has, for example, 128 bits. Details of the individualidentifiers are as follows.

[0074] The regular position identifier is assigned to each sub-network.The regular position identifier (for example, “G1m1” assigned to node M1in FIG. 1) is formed by interconnecting a network identifier used in thefirst communication (hereinafter referred to as a “regular networkidentifier”) and an interface identifier.

[0075] The compatible position identifier is assigned to eachsub-network, as in the regular position identifier, and the networkidentifier used in the second communication by the mobile node 3 isreferred to as a “mobile guaranteed real network identifier”. Thecompatible position identifier (for example, “L1i1” assigned to node Min FIG. 1) is formed by interconnecting the mobile guaranteed realnetwork identifier and the node identifier. The compatible positionidentifier becomes valid as the network address format, and is unique onthe network.

[0076] A virtual network prefix assigned to mobile nodes is referred toas a “mobile guaranteed general network identifier”. The compatible nodeidentifier (for example, “Oi1” assigned to node M1 in FIG. 1) is formedby interconnecting the mobile guaranteed general network identifier andthe node identifier. The compatible node identifier becomes valid as thenetwork address format, and is unique on the network.

[0077] The network layer address employed in this embodiment can bedetermined whether it is a regular position identifier, a compatiblenode identifier, or a compatible position identifier by the value of thenetwork identifier contained in the network layer address. That is, thespace of the network identifier has been defined so that the networkidentifier of each node is a regular network identifier, a mobileguaranteed general network identifier, or a mobile guaranteed realnetwork identifier by referring to the value of the network identifier.

[0078] In this embodiment, only the single mobile guaranteed generalnetwork identifier is determined (namely, all the mobile nodes have thesame mobile guaranteed general network identifier). However, a pluralityof mobile guaranteed general network identifier may be provided, inwhich case, they may be used as required, and it is also possible toexecute further control by the values of the mobile guaranteed generalnetwork identifiers. For example, the value of a mobile guaranteedgeneral network identifier may indicate the version of the correspondingmobile node so as to perform different types of processing.

[0079] Details of the individual identifiers used in the example of thenetwork shown in FIG. 1 are given below.

[0080] The following values are already predetermined.

[0081] The mobile guaranteed general network identifier has apredetermined value O (64 bits). The regular network identifier G1 (64bits) and the mobile guaranteed real network identifier L1 (64 bits) areassigned to the sub-network N1. The regular network identifier G2 (64bits) and the mobile guaranteed real network identifier L2 are assignedto the sub-network N2. The regular network identifier G3 and the mobileguaranteed real network identifier L3 are assigned to the sub-networkN3.

[0082] The mobile node M1 has the node identifier i1 (64 bits) and theinterface identifier m1 (64 bits). The compatible node identifier of themobile node M1 is “Oi1” (128 bits), which is fixed regardless of towhich network the mobile node M1 is connected. When being connected tothe sub-network N1, the mobile node M1 acquires the regular networkidentifier G1 and the mobile guaranteed real network identifier L1. Inthis case, the current regular position identifier of the mobile node M1is G1m1 (128 bits), while the current compatible position identifierthereof is L1i1 (128 bits).

[0083] It is now assumed that an IPv6 network is used in thisembodiment. When

[0084] m1 is 0000:39ff:fe00:0001 (64 bits),

[0085] i1 is 1000:a000:b000:c000 (64 bits),

[0086] G1 is 3ffe:0501:1000:2000 (64 bits), and

[0087] O is fe00:0000:0000:0000 (64 bits), the current positionidentifier (G1m1) of the mobile node is3ffe:0501:1000:2000:0000:39ff:fe00:0001, and the current compatibleposition identifier (Oi1) thereof isfe00:0000:0000:0000:1000:a000:b000:c000.

[0088] One example of the binding information when the values of theidentifiers of the mobile node M1 are set as above is shown in FIG. 2.

[0089] As in the case of the mobile node M1, a mobile node M2 has a nodeidentifier i2 (64 bits) and an interface identifier m2 (64 bits). Thecompatible node identifier of the mobile node M2 is Oi2 (128 bits).

[0090] When being connected to the sub-network N3, the mobile node M2acquires the regular network identifier G3 and the mobile guaranteedreal network identifier L3. In this case, the current regular positionidentifier of the mobile node M2 is G3m2 (128 bits) and the currentcompatible position identifier thereof is L3i2 (128 bits).

[0091] One example of the binding information when the values of theidentifiers of the mobile node M2 are set above is shown in FIG. 3.

[0092] A fixed node C1 has an interface identifier c1 (64 bits). Whenconnected to the sub-network N3, the fixed node C1 acquires the regularnetwork identifier G3, in which case, the regular position identifier ofthe fixed node C1 is G3c1 (128 bits).

[0093] Likewise, a fixed node C2 has an interface identifier c2 (64bits). When connected to the sub-network N2, the fixed node c2 acquiresthe regular network identifier G2, in which case, the regular positionidentifier of the fixed node c2 is G2c2 (128 bits).

[0094] As discussed above, a mobile node possesses therein a mobileguaranteed general network identifier, a node identifier, and aninterface identifier. When being connected to a network, the mobile nodeis able to acquire a mobile guaranteed real network identifier and aregular network identifier, and to use a compatible nodeidentifier/compatible position identifier and a regular positionidentifier.

[0095] On the other hand, a fixed node possesses therein an interfaceidentifier, and when being connected to a network, it is able to acquirea regular network identifier and to use a regular position identifier.

[0096] A description is now given of the configuration and operation ofthe position identifier processing apparatus loaded in each of thebinding server and the mobile node.

[0097]FIG. 4 illustrates an example of the configuration of the bindingserver 2. The binding server 2 includes, as shown in FIG. 4, a bindingstorage unit 21, a binding registration receiver 22, and a bindingresponse unit 23.

[0098] The binding storage unit 21 stores the binding information (seeFIGS. 2 and 3) including the compatible node identifier, the currentcompatible position identifier, and additional information (in thisexample, the registered time and the effective period) concerning themobile nodes under the control of the binding server 2.

[0099] The binding registration receiver 22 receives a registrationrequest concerning the binding from a mobile node.

[0100] The binding response unit 23 responds to a query about thebinding of a certain mobile node.

[0101] The mobile node 3 is provided, as shown in FIG. 1, with theposition identifier processing apparatus 31. Obviously, the mobile node3 is provided with other devices required for performing datacommunication via a network, such as an input/output device, acommunication interface, various control software and applicationsoftware. Such devices are, however, well known, and an explanationthereof will thus be omitted.

[0102]FIG. 5 illustrates an example of the configuration of the positionidentifier processing apparatus 31 of the mobile node 3.

[0103] The position identifier processing apparatus 31 is formed of, asshown in FIG. 5, a binding determining unit 311, a binding processor312, a binding temporary storage unit 313, a binding solving unit 314, amovement detector 315, a binding registration unit 316, an IP processor317.

[0104] The binding determining unit 311 determines whether the bindinginformation is to be used, based on the source address (which isdesignated with the network layer address of a sender node) of a packetand the destination address (which is designated with the network layeraddress of a final destination node) of the packet. This determinationis made based on, for example, the sending and receiving addresses, andmore specifically, by referring to the network identifiers (for example,G1 through G3, L1 through L3, and O) contained in the addresses.

[0105] The binding processor 312 converts the compatible node identifier(for example, Oi2) which is used in an upper layer, for example, anapplication, and the compatible position identifier (for example, L3i2)which is used in performing packet transfer in a network.

[0106] The binding temporary storage unit 313 manages the bindinginformation (see FIGS. 2 and 3) of the mobile node 3 and the othernodes. The binding temporary storage unit 313 has a cache function ofstoring the binding information (which is the function of storing aplurality of items of binding information concerning the node to whichthe mobile node 3 is currently communicating, and the nodes to which themobile node 3 communicated in the past). If the binding temporarystorage unit 313 does not have required binding information, it is ableto request the binding solving unit 314 to solve the problem of binding.

[0107] The binding solving unit 314 queries the binding server 2 as tothe binding information of a node to which the mobile node 3 iscurrently communicating or is to communicate according to the secondcommunication, and reports the result to the binding temporary storageunit 313.

[0108] The movement detector 315 detects that the mobile node 3 has beenmoved between networks, and reports the compatible position identifierrepresenting the current position on the network to the bindingregistration unit 316.

[0109] Based on the information reported from the movement detector 315,the binding registration unit 316 reports the current bindinginformation to the binding server 2 and registers it in the bindingtemporary storage unit 313.

[0110] The IP processor 317 executes processing concerning the networklayer.

[0111] The functions of the individual components of the binding server2 shown in FIG. 4 are discussed in detail below.

[0112] The binding registration receiver 22 receives a bindingregistration request from a mobile node. The received request isreported to the binding storage unit 21. After completion of theregistration in the binding storage unit 21, the binding registrationreceiver 22 reports a registration response message representing thecompletion of the registration to the mobile node which has requestedthe registration.

[0113] The binding response unit 23 receives a query request concerningthe binding information (for example, Oi1, L1i1, T1, LT1) of a certaincompatible node identifier (for example, Oi1), and makes a query aboutit to the binding storage unit 21. Then, the binding response unit 23receives a response from the binding storage unit 21 and reports it tothe node which has queried about the binding information.

[0114] The binding storage unit 21 stores the binding information (inthis example, the compatible node identifier, the compatible positionidentifier, and the registered time, and the effective period) of themobile nodes which are under the control of the binding server 2. Thebinding storage unit 21 receives such binding information from thebinding registration receiver 22.

[0115] When receiving a registration request from the bindingregistration receiver 22, the binding storage unit 21 determines whetherthe source node is a mobile node. If so, the binding storage unit 21further determines whether the mobile node is a valid node, and if themobile node is authenticated, the binding storage unit 21 registers thereceived binding information (new registration or updating). In thiscase, the binding storage unit 21 further checks for a mobile node whichhas sent a registration request and which is under the control of notonly the binding server 2 but also another binding server. This can bechecked by referring to the compatible node identifier of the mobilenode and by making a query to the binding server 2 or a predeterminedserver about whether such a server is present, and if so, about theaddress of the binding server. If the presence of such a binding serveris determined, a binding registration request similar to that sent tothe binding server 2 is sent to the corresponding binding server.

[0116] If a binding registration request has been sent from anotherbinding server, the binding storage unit 21 first authenticates thebinding server and then registers the received binding information (newregistration or updating).

[0117] In response to a query from the binding response unit 23, thebinding storage unit 21 reports the binding information of the requestedcompatible node identifier.

[0118] Additionally, the binding storage unit 21 erases the bindinginformation which has expired.

[0119] For example, it is now assumed in FIG. 1 that binding servers B11and B12 are assigned to the mobile node M1 and binding servers B21 andB22 are assigned to the mobile node M2, and that the mobile node M1sends a binding registration request to one of the binding servers B11and B12 (for example, B11). Then, the binding server B11 stores thebinding information (see FIG. 2) of the mobile node M1 and also sendsthe same information to the binding server B12. This enables the bindingserver B12 to retain the binding information of the mobile node M1. Bymaking a query to one of the binding servers B11 and B12, a mobilecomputer is able to acquire the binding information of the mobile nodeM1 having the compatible node identifier Oi1. The same applies to therelationship between binding servers B21 and B22 and the mobile node M2.

[0120] A detailed description is now given of the functions of theindividual components of the position identifier processing apparatus 31of the mobile node 3 shown in FIG. 5.

[0121] The operation of the IP processor 317 is briefly given below. Insending and receiving packets, the IP processor 317 generates an IPpacket based on transfer data and the destination address received froman upper layer, and then delivers it to the datalink layer (after beingsubjected to certain processing in the datalink layer, the packet issent to a network). In receiving packets, after a packet transferred viaa network has been subjected to certain processing in the datalinklayer, the IP processor 317 extracts the data and the source addressfrom the IP packet received from the datalink layer, and delivers it toan upper layer.

[0122] That is, in this embodiment,

[0123] (a-1) in transmitting a packet, if the regular positionidentifier is specified as the destination address by an upper layer,such as the application, the packet is transmitted by using the regularposition identifier;

[0124] (a-2) in transmitting a packet, if the compatible node identifieris specified as the destination address by an upper layer, such as theapplication, the packet is transmitted by using the compatible positionidentifier;

[0125] (b-1) in receiving a packet, if the regular position identifiersare designated as the source and destination addresses, they aredelivered, together with the data contained in the packet, to an upperlayer, such as the application; and

[0126] (b-2) in receiving a packet, if the compatible positionidentifiers are designated as the source and destination addresses, thecompatible node identifiers are delivered, together with the datacontained in the packet, to an upper layer, such as the application.

[0127] For writing the source address into a packet to be transmitted,the following technique may generally be employed. When the destinationaddress is specified by the application, a node queries the IP processorabout an appropriate source address in order to select it from theaddresses possessed by the node. More specifically, by referring to apath table, an address which matches the conditions is selected from theaddresses provided for interfaces through which a packet is to betransmitted, or if such an address cannot be detected, all the addressespossessed by the node are searched. In this case, if the destinationaddress specified by the application indicates a compatible nodeidentifier, the compatible node identifier of the node is alsodesignated as the source address. If not, a regular position identifieris specified as the source address. Thereafter, both the source anddestination addresses are specified from an upper layer to the IP layer.

[0128] In this embodiment, for writing the source address into a packetto be transmitted, the following techniques may be considered.

[0129] (1) In the IP processor 317, the destination address receivedfrom an upper layer is written into a packet to be transmitted, andwithout writing the source address, the binding determining unit 311 isoperated (as a result, if the destination address is a compatible nodeidentifier, it is overwritten by a compatible position identifier by thebinding processor 312). If the IP processor 317 receives a message fromthe binding determining unit 311 that the destination address is acompatible position identifier, it writes a compatible positionidentifier into the source address. Conversely, if the destinationaddress is found to be a regular position identifier, the IP processor317 writes a regular position identifier into the source address.

[0130] (2) In the IP processor 317, the destination address receivedfrom an upper layer is written into a packet to be transmitted, and aregular identifier is temporarily written into the packet as the sourceaddress. Then, the binding determining unit 311 is operated (as aresult, if the destination address is a compatible node identifier, itis overwritten by the compatible position identifier by the bindingprocessor 312). If the IP processor 317 receives a message from thebinding determining unit 311 that the destination address is acompatible position identifier, the IP processor 317 overwrites thepreviously written regular position identifier by a compatible positionidentifier as the source address into the packet to be transmitted.

[0131] (3) In the above-mentioned technique (2), a compatible positionidentifier is temporarily written as the source address.

[0132] (4) In the IP processor 317, the destination address receivedfrom an upper layer is written into a packet to be transmitted, and aregular position identifier is temporarily written as the sourceaddress. Then, the binding determining unit 311 is operated. As aresult, if the destination address is a compatible node identifier, thebinding processor 312 is activated. The source and destination addressesare overwritten by compatible position identifiers by the bindingprocessor 312, and the packet having the compatible position identifiersas the source and destination addresses is returned to the IP processor311.

[0133] In this embodiment, techniques (1) and (4) are employed by way ofexample.

[0134] In receiving packets, before executing the processing by the IPprocessor 317, or upon completion of the predetermined processing by theIP processor 317, the source and destination addresses of a packet to bereceived which are compatible position identifiers are converted intocompatible node identifiers. In this case, only the source address maybe converted into a compatible node identifier. Alternatively, aftercompleting the whole processing by the IP processor 317, the compatibleposition identifiers may be converted into compatible node identifiersbefore the packet is sent to an upper layer.

[0135] In transmitting a packet, the binding determining unit 311 checksthe address format of the destination address of a packet to betransmitted by the IP processor 317, and if the address format of thedestination address is a compatible node identifier, the packet isdelivered to the binding processor 312. According to the above-describedtechnique (1), after the destination address which is a compatible nodeidentifier is converted into a compatible position identifier by thebinding processor 312, the binding determining unit 311 reports to theIP processor 317 that the destination address was a compatible nodeidentifier, and also returns the resulting packet to the IP processor317. On the other hand, according to the above-described technique (4),the destination address which is a compatible node identifier isconverted into a compatible position identifier by the binding processor312, and also, the compatible position identifier of the node 3 (in thiscase, mobile node M1) is written as the source address. The bindingdetermining unit 311 then returns the resulting packet to the IPprocessor 317, as will be discussed below.

[0136] If the binding determining unit 311 receives a message from thebinding processor 312 that there is no corresponding bindinginformation, the processing of the IP processor 317 is interrupted.

[0137] If the address format of the destination address is found to be aregular position identifier, the binding processor 312 is not activated.According to the aforementioned technique (1), the binding determiningunit 311 directly returns the packet to the IP processor 317, andreports to the IP processor 317 that the destination address is aregular position identifier. According to the aforementioned technique(4), the packet is returned to the IP processor 317.

[0138] In receiving packets, the binding determining unit 311 checks theaddress format of the source and destination addresses of the receivedpacket. If the source and destination addresses are found to becompatible position identifiers, the binding determining unit 311delivers the packet to the binding processor 312. The binding processor312 then converts the compatible position identifiers into compatiblenode identifiers, and delivers the resulting packet to the IP processor317.

[0139] If the address format of the source and destination addresses isfound to be the regular position identifier, the binding determiningunit 311 directly delivers the packet to the IP processor 317.

[0140] As will be discussed below, upon receiving a message from thebinding processor 312 indicating that the compatible node identifier isnot valid, the binding determining unit 311 interrupts processing of theIP processor 317.

[0141] In sending and receiving packets between the IP processor 317 andthe binding determining unit 311, instead of transferring data, apointer indicating the storage location of a packet may be delivered. Ifthere is no change in the storage location of the packet, the pointer ismerely delivered from the IP processor 317 to the binding determiningunit 311, and only required messages are sent from the bindingdetermining unit 311 to the IP processor 317. The same applies to datatransfer between other units, such as between the binding processor 312and the binding determining unit 311.

[0142] Upon receiving the packet to be transmitted from the bindingdetermining unit 311, the binding processor 312 extracts the compatiblenode identifier from the destination address of the packet, and queriesthe binding temporary storage unit 313 about the binding information byusing the compatible node identifier as a key. According to theabove-described technique (1), after acquiring the binding informationfrom the binding temporary storage unit 313, the binding processor 312converts the destination address of the packet from the compatible nodeidentifier (for example, Oi2) to the compatible position identifier (forexample, L3i2). The binding processor 312 then returns the resultingpacket to the binding determining unit 311. In contrast, according tothe above-described technique (4), after acquiring the bindinginformation from the binding temporary storage unit 313, the bindingprocessor 312 changes the destination address of the packet into thecompatible position identifier, and also changes the source address ofthe packet into the compatible position identifier of the mobile nodeM1. The binding processor 312 then returns the resulting packet to thebinding determining unit 311.

[0143] If the corresponding binding information cannot be obtained fromthe binding temporary storage unit 313, the binding processor 312reports the information to the binding determining unit 311.

[0144] The received packet is delivered from the binding determiningunit 311 to the binding processor 312. The binding processor 312extracts the compatible position identifier (for example, L3i2) from thesource address of the packet, and substitutes the mobile guaranteed realnetwork identifier (for example, L3) of the compatible positionidentifier with the mobile guaranteed general network identifier (forexample, O), thereby converting the source address into the compatiblenode identifier (for example, Oi2). The binding processor 312 alsochanges the destination address into the compatible node identifier ofthe mobile node M1.

[0145] Additionally, the binding processor 312 determines whether thecompatible node identifier obtained from the compatible positionidentifier of the source address of the packet is valid. If so, thebinding processor 312 returns the packet to the binding determining unit311 and allows it to continue the receiving processing. If thecompatible node identifier is found to be invalid, the binding processor312 sends the corresponding information to the binding determining unit311.

[0146] As discussed above, the binding temporary storage unit 313 storesa single or a plurality of items of binding information, and also erasesthe binding information which has expired. In response to a request fromthe binding processor 312, the binding temporary storage unit 313returns the binding information of the requested compatible nodeidentifier.

[0147] If there is no binding information of the requested compatiblenode identifier, the binding temporary storage unit 313 requests thebinding solving unit 314 to acquire the required binding informationfrom the binding server 2.

[0148] If the required binding information cannot be acquired from thebinding server 2, the binding temporary storage unit 313 sends thecorresponding message to the binding processor 312.

[0149] When being requested from the binding temporary storage unit 313to search for the binding information, the binding solving unit 314searches for an appropriate binding server from the designatedcompatible node identifier, and requests the binding server to send thebinding information (if more than one binding servers are searched, thesuitable binding server is selected). For example, in the example shownin FIG. 1, when obtaining the binding information of the mobile node M2with which the mobile node M1 is to communicate, the mobile node M1queries one of the binding servers B11 and B12, which are assigned tothe mobile node M2, about the binding information.

[0150] If the required information is obtained from the binding server2, it is stored in the binding temporary storage unit 313. If not, thebinding solving unit 314 sends the corresponding message to the bindingtemporary storage unit 313.

[0151] The movement detector 315 stores, for example, the regularnetwork identifier acquired in the sub-network to which the mobile nodeM1 was last connected, and compares a newly acquired regular networkidentifier (this operation is performed even if no regular networkidentifier is stored because the mobile node M1 has never been connectedbefore). If the previous regular network identifier does not coincidewith the new regular network identifier, the movement detector 315determines that the mobile node M1 has been moved between networks. Forexample, when the mobile node M1 has been moved from the sub-network N2to the sub-network N1, the regular network identifier is changed from G2to G1. The movement detector 315 then detects inconsistencies of theregular network identifiers, thereby recognizing that the mobile node M1has been moved between the networks.

[0152] Then, the movement detector 315 detects the mobile guaranteedreal network identifier used in the network to which the node M1 hasbeen moved. For example, in the example shown in FIG. 1, the mobileguaranteed real network identifier L1 is detected.

[0153] Subsequently, the movement detector 315 generates the compatibleposition identifier (for example, L1i1) from the detected mobileguaranteed real network identifier (for example, L1) and the nodeidentifier (for example, i1) of the mobile node M1. It should be notedthat the compatible node identifier (for example, Oi1) consisting of themobile guaranteed general network identifier and the node identifier isfixed.

[0154] The movement detector 315 reports the generated compatibleposition identifier to the binding registration unit 316. The movementdetector 315 also reports to the IP processor 317 as required that thegenerated compatible position identifier should also be used as aposition identifier of the mobile node M1.

[0155] The binding registration unit 316 searches for a group of bindingservers which are suitable for the mobile node M1, and temporarilystores a position (network layer address) of one or a plurality ofdetected binding servers. This operation is performed regularly.

[0156] The binding registration unit 316 generates the latest bindinginformation (see FIG. 2) by using the compatible position identifier(for example, L1i1) reported from the movement detector 315, and sends aregistration request message including the latest binding information toone of the binding servers (for example, BA11 in FIG. 1). If more thanone binding servers are assigned to the mobile node M1, the bindingserver which has registered the latest binding information reports thebinding information to the other server (for example, BA12 shown in FIG.1).

[0157] If the registration has failed in one binding server (forexample, BA11 in FIG. 1 is not in operation), the binding registrationunit 316 attempts to register the binding information in another bindingserver (for example, BA12 in FIG. 1).

[0158] The binding registration unit 316 also registers the bindinginformation of the mobile node M1 in the binding temporary storage unit313, or updates the binding information of the mobile node M1 stored inthe binding temporary storage unit 313.

[0159] Alternatively, the binding registration unit 316 may directlysend the latest binding information to a node with which the mobile nodeM1 is currently communicating.

[0160] The operations of the mobile node and the binding server are nowdiscussed by using a specific example.

[0161] A description is given below, with reference to FIG. 6, of theinitial setting when the mobile node 3 is moved, and the processing forsending and receiving packets. The various identifiers and the nodes towhich each server is assigned are similar to those in FIG. 1.

[0162]FIG. 7 is a flow chart illustrating an example of the initialsetting processing when the mobile node 3 is moved.

[0163] It is now assumed that the mobile node M1 is moved betweennetworks and is connected to the sub-network N1 (or, it is initiallyconnected to the sub-network N1), and the time at which the mobile nodeM1 is connected to the sub-network N1 is determined to be time T1 in abuilt-in clock.

[0164] The mobile node M1 acquires the address which matches the regularnetwork identifier. In this example, G1 is obtained as the regularnetwork identifier, resulting in the regular position identifier G1m1.

[0165] By detecting that the stored regular network identifier does notcoincide with the latest network identifier G1 (or the previous regularnetwork identifier does not exist), in step S1, the movement detector315 of the mobile node M1 detects that the mobile node M1 has beenmoved.

[0166] Then, in step S2, the movement detector 315 detects the mobileguaranteed real network identifier L1 usable in the sub-network to whichthe mobile node M1 is currently connected. In step S3, the movementdetector 315 generates the compatible position identifier L1i1 from themobile guaranteed real network identifier L1 and the node identifier i1.

[0167] In step S4, the movement detector 315 then reports the generatedcompatible position identifier L1i1 to the binding registration unit316.

[0168] Subsequently, the binding registration unit 316 generates bindinginformation and registers it in the binding temporary storage unit 313of the mobile node M1. Alternatively, the binding registration unit 316updates the binding information stored in the binding temporary storageunit 313.

[0169] For registering the binding information in the binding server instep S5, the binding registration unit 316 first specifies the positionof the binding server which is assigned to the mobile node M1.

[0170] This is discussed more specifically by referring to a domain namesystem (DNS).

[0171] A DNS server corresponding to the compatible node identifier of amobile node is prepared. A record format representing the bindingservers is newly added to the DNS server. In this example, in the DNSserver corresponding to the compatible node identifier Oi1 of the mobilenode M1, as a record of binding servers corresponding to the compatiblenode identifier Oi1, B11 and B12 are registered. Similarly, for a DNSserver corresponding to the compatible node identifier Oi2 of the mobilenode M2, as a record of binding servers corresponding to the compatiblenode identifier Oi2, B21 and B22 are registered.

[0172] The binding registration unit 316 of the mobile node M1 queriesthe appropriate DNS server about the binding servers corresponding tothe compatible node identifier Oi1 of the mobile node M1.

[0173] In response to the query from the mobile node M1, the DNS servertraces the DNS tree to detect the DNS server which manages thecompatible node identifier Oi1. If the detected DNS server is found tobe the DNS server which has received the query from the mobile node M1,the DNS server returns the answer, that is, the binding servers B11 andB12, to the mobile node M1.

[0174] If the DNS server which manages the compatible node identifierOi1 is found to be a DNS server other than the DNS server which hasreceived the query from the mobile node M1, the latter DNS serverqueries the detected DNS server about the binding server correspondingto the compatible node identifier Oi1. The detected DNS server thenreturns the answer, that is, the binding servers B11 and B12, to therequested DNS server. Then, the DNS server which has received therequest from the mobile node M1 returns the same answer, that is, B11and B12, to the mobile node M1.

[0175] Subsequently, in step S6, the mobile node M1 selects one of thebinding servers B11 and B12, and sends a registration request messagecontaining the latest binding information (Oi1, L1i1, T1, and LT1) tothe selected binding server (in this example, B11) (see p1 in FIG. 6).As stated above, T1 indicates the time at which the mobile detector 315detected that the mobile node M1 was moved), and LT1 represents theeffective period of the binding information.

[0176] After the mobile node M1 sends a registration request messageincluding the latest binding information to the binding server B11, thebinding registration receiver 22 of the binding server B11 receives thismessage (see p1 in FIG. 6). The binding registration receiver 22 thenreports this registration content to the binding storage unit 21. Thebinding storage unit 21 determines whether the sender is the mobile nodeM1. If the sender is authenticated, the binding storage unit 21 adds thereceived information to the currently stored information, or updates theinformation of the mobile node M1. Then, the binding storage unit 21informs the completion of the registration to the mobile node M1 (see p1in FIG. 1), and the mobile node M1 receives this message.

[0177] Subsequently, the binding server B11 specifies the position ofanother binding server which manages the mobile node M1. In thisexample, the binding server B11 detects the position of the bindingserver B12, and thus sends the received binding information of themobile node M1 to the binding server B12 (see p11 in FIG. 6).

[0178] Upon receiving the binding information from the binding serverB11, the binding server B12 checks whether this binding information hasbeen sent from the mobile node M1. The binding server B12 firstdetermines whether the binding information is sent from the bindingserver B11. If so, the binding server B12 searches the bindinginformation stored in the binding server B12 for the informationconcerning the compatible node identifier Oi1. If so, the time of thedetected binding information is compared with that received from thebinding server B11. If the time of the received information is found tobe later, the information is updated by this information. If not, thereceived information from the binding server B11 is discarded.

[0179] The same applies to when the mobile node M2 is connected to thesub-network N3 at time T2.

[0180] The same also applies to when the mobile node M1 sends aregistration request containing the latest binding information to thebinding server B12 and when the binding server B12 sends the sameregistration content to the binding server B11.

[0181] The mobile node M1 is now able to use the regular positionidentifier G1m1 and the compatible position identifier L1i1 as theposition identifiers of the mobile node M1. This enables the othermobile nodes, such as the mobile node M2, to search for the currentcompatible position identifier L1i1 by querying the binding server.

[0182] Similarly, the mobile node M2 is able to use the regular positionidentifier G3m2 and the compatible position identifier L3i2 as theposition identifiers of the mobile node M2. This enables the othermobile nodes, such as the mobile node M1, to search for the currentcompatible position identifier L3i2 of the mobile node M2 by queryingthe binding server.

[0183] In this case, the binding information of the mobile node M1stored in the binding servers B11 and B12 can be indicated by the oneshown in FIG. 2. Likewise, the binding information of the mobile node M2stored in the binding servers B21 and B22 can be indicated by the oneshown in FIG. 3.

[0184] A description is given below, with reference to FIG. 6, thesecond communication performed between the mobile node M1 which hasregistered the latest binding information when being connected to thesub-network N1 and the mobile node M2 connected to the sub-network N3.In this example, a packet is to be transmitted from the mobile node M1to the mobile node M2.

[0185] An example of the packet transmitting processing performed by themobile node M1 is discussed below with reference to FIG. 8.

[0186] The user of the mobile node M1 specifies the compatible nodeidentifier Oi2 as the IP address so as to communicate with the mobilemode M2. After a packet to be transmitted from the mobile node M1 to themobile node M2 is generated, the binding determining unit 311 of themobile node M1 receives the packet. Then, in step S11, the bindingdetermining unit 311 determines whether the destination address to betransmitted is a regular position identifier or a compatible nodeidentifier.

[0187] In this example, since the destination address is Oi2, whichcontains the mobile guaranteed general network identifier O, the bindingdetermining unit 311 determines that the destination address is acompatible node identifier, in other words, the binding determining unit311 determines that the second communication is to be performed, anddelivers the packet to the binding processor 312.

[0188] In step S12, the binding processor 312 then searches for thecompatible position identifier corresponding to the above-mentionedcompatible node identifier.

[0189] More specifically, the binding processor 312 first queries thebinding temporary storage unit 313 as to the binding informationconcerning the compatible node identifier Oi2 designated as thedestination address. If the corresponding binding information is storedin the binding temporary storage unit 313, the binding temporary storageunit 313 returns it to the binding processor 312. In this example,however, the packet to be transmitted to the mobile node M2 is the firstpacket addressed to the mobile node M2, the binding temporary storageunit 313 does not store binding information concerning the compatiblenode identifier Oi2 of the mobile node M2. Thus, the binding processor312 requests the binding solving unit 314 to acquire the bindinginformation concerning the compatible node identifier Oi2.

[0190] In response to this request, the binding solving unit 314 firstsearches for the binding servers which are assigned to the compatiblenode identifier Oi2. As a result, in this example, the positions of thebinding servers B21 and B22 are detected. The binding solving unit 314then queries one of the binding servers B21 and B22 (in this case, thebinding server B21) about the binding information of the compatible nodeidentifier oi2 (see p2 in FIG. 6).

[0191] The binding response unit 23 of the binding server B21 receivesthe query from the mobile node M1, and requests the binding storage unit21 to extract the binding information of the compatible node identifierOi2. Since the binding server B21 stores the information shown in FIG.3, the binding storage unit 21 reports the binding information Oi2,L3i2, T2, and LT2 to the binding response unit 23. The binding responseunit 23 then notifies this binding information to the mobile node M1(see p2 in FIG. 6).

[0192] Upon receiving the binding information from the binding serverB21, the binding solving unit 314 of the mobile node M1 reports it tothe binding temporary storage unit 313.

[0193] The binding temporary storage unit 313 receives the bindinginformation and stores it therein, and then transfers this bindinginformation to the binding processor 312, which is waiting for theanswer.

[0194] Upon receiving the binding information, in step S13, the bindingprocessor 312 changes the destination address from the compatible nodeidentifier Oi2 to the compatible position identifier L3i2, and when theabove-described technique (4) is employed, the binding processor 312writes the compatible position identifier L1i1 of the mobile node M1into the source address of the packet to be transmitted. Then, thebinding processor 312 delivers this packet to the IP processor 317. Ifthe aforementioned technique (1) is employed rather than technique (4),the binding processor 312 informs the IP processor 317 that thedestination address of the packet is a compatible position identifier,and the IP processor 317 changes the source address of the packet intothe compatible position identifier L1i1 of the mobile node M1.

[0195] Ultimately, in step S14, the packet having the compatibleposition identifier L1i1 as the source address and the compatibleposition identifier L3i2 as the destination address is transmitted fromthe mobile node M1 to the mobile node M2 (see p3 in FIG. 6). However,the destination address of the mobile node M2 identified by the mobilenode M1 still remains as the compatible node identifier Oi2 rather thanthe compatible position identifier L3i2. This is unchanged regardless ofto which network the mobile node M2 is connected.

[0196] In sending another packet from the mobile node M1 to the mobilenode M2, it is no longer necessary for the mobile node M1 to query thebinding server about the binding information concerning the mobile nodeM2 since the binding temporary storage unit 313 already stores thebinding information. The mobile node M1 thus simply generates a packethaving the compatible position identifier L1i1 as the source address andthe compatible position identifier L3i2 as the destination addressaccording to the binding information stored in the binding temporarystorage unit 313, and sends the packet to the mobile node M2.

[0197] An example of the packet receiving processing is discussed belowwith reference to FIG. 9.

[0198] In step S21, the packet transmitted from the mobile node M1 isdelivered to the network position specified by the destination addressL3i2 and reaches the mobile node M2 (see p4 in FIG. 6).

[0199] Subsequently, in step S22, the binding determining unit 311 ofthe mobile node M2 checks the source address and the destination addressof the received packet. Since both the source address L1i1 and thedestination address L3i2 contain mobile guaranteed real networkidentifiers, the binding determining unit 311 determines that the sourceaddress and the destination address are compatible position identifiers,in other words, the binding determining unit 311 determines that thesecond communication is being performed, and delivers the receivedpacket to the binding processor 312.

[0200] In step S23, the binding processor 312 of the mobile node M2substitutes the mobile guaranteed real network identifiers of the sourceand destination addresses by the mobile guaranteed general networkidentifiers, thereby converting the compatible position identifiers intothe compatible node identifiers. In this example, the source address isconverted into Oi1 and the destination address is converted into Oi2.

[0201] In step S24, the binding processor 312 then determines whetherthe relationship between the compatible position identifier L1i1 set asthe source address and the compatible node identifier Oi1 converted fromthe received source address is valid.

[0202] For example, when the packet is provided with an authenticator,the binding processor 312 checks whether the authenticator is valid. Ifso, the binding processor 312 determines that the relationship betweenthe compatible node identifier and the compatible position identifier isvalid. When an authenticator is not attached to the packet, the bindingprocessor 312 may query the binding temporary storage unit 313 about thebinding information of the compatible node identifier Oi1. In this case,if the binding information obtained from the binding temporary storageunit 313 coincides with the relationship between the compatible nodeidentifier and the compatible position identifier determined from thereceived packet, the source address is authenticated. If theabove-described two items of information do not coincide with eachother, the binding processor 312 requests the binding temporary storageunit 313 to acquire the latest binding information (from the bindingserver) once again. If the binding information received from the bindingserver does not coincide with the relationship between the compatiblenode identifier and the compatible position identifier, the bindingprocessor 312 determines that the received packet has not been sent froma mobile node provided with the compatible node identifier Oi1. Thus,authentication has failed. If the above-mentioned two items ofinformation coincide with each other, authentication has succeeded.

[0203] If authentication has succeeded, in step S25, the packet isdelivered from the binding processor 312 to the IP processor 317, andthe receiving processing is allowed to continue. If authentication hasfailed, the packet is discarded, and the receiving processing performedby the IP processor 317 is interrupted.

[0204] As for the case of the mobile node M1, the source addressidentified by the mobile node M2 is the compatible node identifier Oi1rather than the compatible position identifier L1i1.

[0205] The detection of the movement of a mobile node by another mode isdiscussed below with reference to FIG. 10. It is now assumed in thatFIG. 10 illustrates a network in which the mobile node M1 and the mobilenode M2 shown in FIG. 6 are performing the second communication.

[0206]FIG. 11 illustrates an example of the processing for detecting themovement of a mobile node by another mobile node while communication isbeing performed between the two nodes.

[0207] During the second communication which supports the movement ofmobile nodes, i.e., when performing communication while performingconversion between a compatible node identifier and a compatibleposition identifier by using binding information, it is assumed that anerror message is returned to the mobile node which has sent a packet,indicating that the packet has not reached the destination address. Inthis case, the destination mobile node may have been moved. Uponreceiving the error message, the sender mobile node obtains the latestbinding information from the destination mobile node, thereby restartingthe communication.

[0208] For example, the mobile node M1 connected to the sub-network N1and the mobile node M2 connected to the sub-network N3 were performingthe second communication, as shown in FIG. 6, and then, the mobile nodeM2 has been moved to the sub-network N2, as shown in FIG. 10. The mobilenode M1 sends a packet addressed to the mobile node M2 to thesub-network N3 without knowing that the mobile node M2 has been moved tothe sub-network N2.

[0209] After being moved to the sub-network N2, the mobile node M2reports the latest binding information (for example, Oi2, L2i2, T3, andLT3) of the mobile node M2 to the binding node (for example, B21)assigned to the mobile node M2 (see p21 in FIG. 10). The binding nodeB21 then reports the latest binding information to the binding node B22(see p22 in FIG. 10).

[0210] However, if L3i2 still remains in the binding temporary storageunit 313 of the mobile node M1 as the current compatible positionidentifier of the mobile node M2, the mobile node M1 sends a packethaving the compatible position identifier L3i2 as the destinationaddress to the mobile node M2 (see p31 in FIG. 10).

[0211] The packet reaches the router (not shown) connected to thesub-network N3. However, since the mobile node M2 has been moved to thesub-network N2, the router detects after the lapse of a predeterminedperiod that there is no node having the address L3i2 in the sub-networkN3. In this case, the router returns an error message to the mobile nodeM1 indicating that the packet has not reached the node M2 (see p311 inFIG. 10.

[0212] Upon receiving this error message, in step S31, the mobile nodeM1 detects that the mobile node M2 has been moved from the sub-networkN3.

[0213] Then, the mobile node M1 first nullifies the binding informationof the mobile node M2 stored in the binding temporary storage unit 313,and also makes a query about the binding information concerning thecompatible node identifier Oi1. In this case, the binding temporarystorage unit 313 requests the binding solving unit 314 to acquire therequired binding information from the binding server. If the mobile nodeM2 has been moved as discussed above, in step S32, the bindinginformation reflecting the correct current position of the mobile modeM2 is obtained from the binding server B21 or B22 (see p32 in FIG. 10).

[0214] Upon receiving the latest binding information (for example, Oi2,L2i2, T3, and LT3), the binding temporary storage unit 313 is requestedto update the previous binding information by the latest information.Then, in step S33, the binding processor 312 restarts the transmittingprocessing by changing the destination address of the packet into thenew compatible position identifier L2i2 of the mobile node M2, andre-transmits the packet having the compatible position identifier L2i2as the destination address (see p33 in FIG. 10).

[0215] If the mobile node M2 is not connected to any network, or if thelatest binding information is not registered in the binding serverassigned to the mobile node M2 even if the mobile node M2 is connectedto a network, the mobile node M1 discontinues communication with themobile node M2, or repeats the above-described processing after thelapse of a predetermined period.

[0216] The first communication performed between mobile nodes isdescribed below with reference to FIG. 12. Various identifiers and anode to which each server is assigned are similar to those in theexample in FIG. 1.

[0217] It may sometimes be desired that a mobile node performs the firstcommunication with another mobile node for detecting a failure even ifthey are capable of performing the second communication. In this case,as the IP address designated as the destination node, a regular positionidentifier is used rather than a compatible position identifier. Uponreceiving a packet, the receiver node detects that the source anddestination addresses of the received packet are regular positionidentifiers, and thus performs the first communication.

[0218] The processing for transmitting a packet when the firstcommunication is performed between mobile nodes is discussed below withreference to FIG. 8.

[0219] The user of the mobile node M1 specifies the regular positionidentifier G3m2 as the IP address so as to communicate with the mobilenode M2. After generating a packet to be transmitted from the mobilenode M1 to the mobile node M2, the binding determining unit 311 of themobile node M1 receives the packet. In step S11, the binding determiningunit 311 determines whether the destination address of the packet is aregular position identifier or a compatible node identifier. In thisexample, since the destination address is G3m2, which does not containthe mobile guaranteed general network identifier O, the bindingdetermining unit 311 determines that the destination address is aregular position identifier, in other words, the binding determiningunit 311 determines that the first communication is to be performed.Thus, the transmitting processing is continued without converting theaddresses using the binding information.

[0220] Accordingly, in this case, in step S15, the packet having theregular position identifier G1m1 as the source address and the regularposition identifier G3m2 as the destination address is transmitted fromthe mobile node M1 to the mobile node M2 (see p41 in FIG. 12).

[0221] The processing for receiving a packet when the firstcommunication is performed between mobile nodes is described below withreference to FIG. 9.

[0222] In step S21, the packet transmitted from the mobile node M1 asdiscussed above is delivered to the network position designated by thedestination address G3m2 and reaches the mobile node M2 (see p41 in FIG.12).

[0223] In step S22, the binding determining unit 311 of the mobile nodeM2 determines whether the source address and the destination address ofthe received packet are regular position identifiers or compatible nodeidentifiers. Since the source address G1m1 and the destination addressG3m2 do not contain a mobile guaranteed real network identifier, thebinding determining unit 311 determines that the source and destinationaddresses of the packet are regular position identifiers, in otherwords, the binding determining unit 311 determines that the firstcommunication is being performed.

[0224] In step S26, the packet having the regular position identifiersas the source and destination addresses is then received.

[0225] Communication performed from a mobile node to a fixed node isdiscussed below with reference to FIG. 12.

[0226] In transmitting a packet from a mobile node to a fixed node,regular position identifiers are specified as the source and destinationaddresses, and thus, the first communication is to be conducted (see p42in FIG. 12).

[0227] This is described more specifically. It is now assumed that apacket is transmitted from the mobile node M1 connected to thesub-network N1 to the fixed node C1 connected to the sub-network N3.

[0228] The processing for transmitting a packet by the mobile node M1 isdiscussed below with reference to FIG. 8.

[0229] The user of the mobile node M1 specifies G3c1 as the IP addressto communicate with the fixed node C1. After generating a packet to betransmitted from the mobile node M1 to the fixed node C1, the bindingdetermining unit 311 of the mobile node M1 receives the packet. Then, instep S11, the binding determining unit 311 determines whether thedestination address of the packet is a regular position identifier or acompatible node identifier. In this example, since the destinationaddress is G3c1, which does not contain the mobile guaranteed generalnetwork identifier O, the binding determining unit 311 determines thatthe destination address is a regular position identifier, in otherwords, the binding determining unit 311 determines that the firstcommunication is to be performed. The transmitting processing is thusexecuted without converting the addresses using the binding information.

[0230] Accordingly, in step S15, the packet having the regular positionidentifier G1m1 as the source address and the regular positionidentifier G3c1 as the destination address is transmitted from themobile node M1. The packet then reaches the fixed node C1 which ispositioned at G3c1 through the network (see p42 in FIG. 12).

[0231] If the mobile node M1 is moved from the sub-network N1,communication from the mobile mode M1 to the fixed node C1 isdiscontinued. As long as the mobile node M1 remains in the sub-networkN1, it is possible to communicate with the fixed node C1.

[0232] A description is now given of the first communication performedfrom a fixed node to a mobile node with reference to FIG. 12.

[0233] A fixed node never uses an address containing a mobile guaranteedreal network identifier. That is, basically, a fixed node does notobtain a compatible position identifier. In transmitting a packet from afixed node to a mobile node, since regular position identifiers arespecified as the source and destination addresses, the firstcommunication is to be performed (see p43 in FIG. 12).

[0234] This is described more specifically. It is now assumed that apacket is to be transmitted from the fixed node C1 connected to thesub-network N3 to the mobile node M1 connected to the sub-network N1.

[0235] The processing for receiving a packet by the mobile node M1 isdiscussed below with reference to FIG. 9.

[0236] The user of the fixed node C1 specifies the regular positionidentifier G1m1 as the destination address to communicate with themobile node M1.

[0237] The packet having the regular position identifier G3c1 as thesource address and the regular position identifier G1m1 as thedestination address is transmitted from the fixed node C1 to thenetwork. Then, in step S21, the packet is received by the mobile node M1(see p43 in FIG. 12).

[0238] In step S22, the binding determining unit 311 of the mobile nodeM2 checks the source address and the destination address of the receivedpacket. Since the source address G3c1 and the destination address G1m1of this packet do not contain a mobile guaranteed real networkidentifier, the binding determining unit 311 determines that the sourceand destination addresses are regular position identifiers, in otherwords, the binding determining unit 311 determines that the firstcommunication is being performed.

[0239] Then, in step S26, the packet having the regular positionidentifiers as the source and destination addresses is received.

[0240] If the mobile node M1 is moved from the sub-network N1,communication between the mobile node M1 and the fixed node C1 isdiscontinued. As long as the mobile node M1 remains in the sub-networkN1, it is possible to communicate with the fixed node C1.

[0241] Between fixed nodes, as shown in FIG. 12, the first communicationusing regular position identifiers is performed (see p44 in FIG. 12).

[0242] More specifically, the user of the fixed node C1 specifies theregular position identifier G2c2 as the destination address of a packetto communicate with the fixed node C2. Then, the packet having theregular position identifier G3c1 as the source address and the regularposition identifier G2c2 as the destination address is transmitted tothe network and reaches the fixed node C2 which is positioned at G2c2.The fixed node C2 then receives this packet.

[0243] Similarly, the user of the fixed node C2 designates the regularposition identifier G3c1 as the destination address of a packet tocommunicate with the fixed node C1. Thus, the packet having the regularposition identifier G2c2 as the source address and the regular positionidentifier G3c1 as the destination address is transmitted from the fixednode C2 to the network and reaches the fixed node C1 which is positionedat G3c1. The fixed node C1 then receives this packet.

[0244] This embodiment has been described, assuming that the format ofthe source address and the format of the destination address are thesame. If they are different, for example, if the source address is aregular position identifier and the destination address is a compatibleposition identifier (other combinations may be considered), thefollowing approaches may be considered: (1) an error message isreturned; (2) the first communication is performed by giving priority tothe regular position identifier; (3) the second communication isperformed by giving priority to the compatible position identifier; and(4) a suitable approach is selected from (1) through (3) or from (2) and(3).

[0245] As discussed above, according to this embodiment, instead ofusing the concept of a home network, which is employed in theconventional mobile IP, a binding server is provided for identifying arelationship between a compatible node identifier which uniquelyspecifies a mobile node and a compatible position identifier whichuniquely specifies the position of the mobile node on a network.Accordingly, binding information concerning a mobile node to becommunicated can be acquired from the binding server, and packets can betransmitted and received while automatically performing conversionbetween a compatible node identifier and a compatible positionidentifier. It is thus possible to enhance redundancy of the bindingserver. Additionally, the need for using the encapsulating technique canbe eliminated, thereby making it possible to reduce the protocoloverhead while the second communication is performed by using acompatible node identifier/compatible position identifier. A mobilecomputer is able to perform both the first communication using a regularposition identifier and the second communication using a compatible nodeidentifier/compatible position identifier, thereby enablingcommunication between a mobile node and a fixed node.

[0246] The above-described functions may be implemented by software.

[0247] This embodiment may be implemented by a computer-readablerecording medium for storing a program which causes a computer toexecute predetermined means (or which causes a computer to function aspredetermined means, or causes a computer to implement predeterminedfunctions).

[0248] The present invention is not restricted to the aforementionedembodiment, and various modifications may be made within the technicalrange of the invention.

What is claimed is:
 1. A position identifier management apparatus forsupporting the movement of a mobile computer between networks,comprising: storage means for storing binding information concerningsaid mobile computer managed by said position identifier managementapparatus, said binding information including a compatible nodeidentifier for uniquely specifying said mobile computer and a compatibleposition identifier for uniquely specifying a position of said mobilecomputer on a network; registration means for registering the bindinginformation in said storage means in response to a registration requestto register the binding information from another apparatus; andtransmitting means for transmitting the binding information in responseto a query about the binding information concerning said mobile computerfrom another apparatus when said binding information is stored in saidstorage means.
 2. A position identifier management apparatus accordingto claim 1 , further comprising: means for registering bindinginformation contained in the received registration request afterdetecting that a sender of the received registration request is anexternal mobile computer and authenticating said external mobilecomputer as a valid mobile computer; means for sending said registrationrequest to an external position identifier management apparatus whichalso manages said external mobile computer when said external mobilecomputer is authenticated as a valid mobile computer; and means forregistering the binding information contained in the receivedregistration request in said storage means after detecting that thesender of the received registration request is an external positionidentifier management apparatus and authenticating said externalposition identifier management apparatus as a valid apparatus.
 3. Aposition identifier management apparatus according to claim 1 , whereinsaid transmitting means transmits the binding information containing thecompatible node identifier which is identical to the compatible nodeidentifier contained in the query.
 4. A position identifier managementapparatus according to claim 1 , wherein the binding informationincludes a registered time and an effective period, and said positionidentifier management apparatus further comprises means for erasing thebinding information which has expired.
 5. A position identifiermanagement apparatus according to claim 1 , wherein the compatible nodeidentifier of said mobile computer comprises a first virtual networkidentifier assigned to said mobile computer which moves between networksand a node identifier for uniquely specifying said mobile computer, andthe compatible position identifier of said mobile computer comprises asecond network identifier which is usable only by mobile computersassigned to a network to which said mobile computer is connected and thenode identifier.
 6. A mobile computer which moves between networks,comprising: first storage means for storing binding informationincluding a compatible node identifier and a compatible positionidentifier, the compatible node identifier including a first virtualnetwork identifier assigned to said mobile computer which moves betweennetworks and a node for uniquely specifying said mobile computer, thecompatible position identifier including a second network identifierwhich is usable only by mobile computers assigned to a network to whichsaid mobile computer is connected and the node identifier; secondstorage means for storing binding information concerning at least one ofexternal mobile computers with which said mobile computer is tocommunicate, said binding information including a compatible nodeidentifier and a compatible position identifier, the compatible nodeidentifier including a first virtual network identifier assigned to saidexternal mobile computer which moves between networks and a nodeidentifier of said external mobile computer, the compatible positionidentifier including a second network identifier which is usable only bymobile computers assigned to a network to which said external mobilecomputer is connected and the node identifier of said external mobilecomputer; determining means for determining whether the bindinginformation is to be used for a packet transmitting or receivingoperation; and conversion means for performing, when said determiningmeans determines that the binding information is to be used, aconversion operation by converting the compatible node identifier to thecompatible position identifier when the packet is to be transmitted andby converting from the compatible position identifier to the compatiblenode identifier when the packet is to be received.
 7. A mobile computeraccording to claim 6 , wherein said determining means determines thatthe conversion operation is to be performed by said conversion meanswhen a destination address of the packet to be transmitted is designatedwith said compatible node identifier.
 8. A mobile computer according toclaim 7 , wherein, when said determining means determines that theconversion operation is to be performed by said conversion means inorder to transmit the packet, said conversion means acquires thecompatible position identifier corresponding to the compatible nodeidentifier which designates the destination address of the packet to betransmitted, and then converts the destination address of the packetinto the acquired compatible position identifier, and sets thecompatible position identifier of said mobile computer stored in saidfirst storage means as a source address of the packet.
 9. A mobilecomputer according to claim 6 , wherein said determining meansdetermines that the conversion operation is to be performed by saidconversion means when a source address and a destination address of thepacket to be received are designated with the compatible positionidentifiers.
 10. A mobile computer according to claim 9 , wherein, whensaid determining means determines that the conversion operation is to beperformed by said conversion means in order to receive the packet, saidconversion means converts the compatible position identifier into thecompatible node identifier by at least substituting the second networkidentifier contained in the compatible position identifier whichdesignates the source address of the packet by the first virtual networkidentifier, and also verifies the integrity of the compatible nodeidentifier which designates the source address of the packet.
 11. Amobile computer according to claim 6 , wherein, when said determinationmeans determines that the conversion operation by said conversion meansis not performed, it is assumed that each of a source address and adestination address of the packet is a position identifier for uniquelyspecifying the position of said mobile computer on a network andcontaining a third network identifier which does not support themovement of said mobile computer, and the packet is transmitted orreceived by using said source address and said destination address. 12.A mobile computer according to claim 6 , further comprising: movementdetection means for detecting the movement of said mobile computer by achange in a third network identifier which does not support the movementdetected on a network to which said mobile computer is connected;acquiring means for acquiring the second network identifier when themovement of said mobile computer is detected; generating means forgenerating new binding information based on the acquired second networkidentifier; and updating means for updating the binding informationconcerning said mobile computer stored in said first storage means bythe new binding information generated by said generating means.
 13. Amobile computer according to claim 12 , further comprising: firstspecifying means for specifying a position identifier managementapparatus which manages said mobile computer from position identifiermanagement apparatuses, disposed on a network, for storing the bindinginformation which is requested to be registered by mobile computersmanaged by said position identifier management apparatuses and forresponding to a query about the binding information; and registrationrequest sending means for sending the new binding information concerningsaid mobile computer generated by said generating means to the positionidentifier management apparatus specified by said first specifyingmeans.
 14. A mobile computer according to claim 6 , further comprising:second specifying means for specifying a position identifier managementapparatus which manages an external mobile computer with which saidmobile computer is to communicate, from position identifier managementapparatuses, disposed on a network, for storing the binding informationwhich is requested to be registered by mobile computers managed by saidposition identifier management apparatuses, and for responding to aquery about the binding information; query sending means for sending,when said second storage means does not store effective bindinginformation about said external mobile computer, a query about thebinding information concerning said external mobile computer containingthe compatible node identifier to the position identifier managementapparatus specified by said second specifying means; response receivingmeans for receiving a response to the query from the position identifiermanagement apparatus specified said second specifying means; andregistration means for registering the binding information concerningsaid external mobile computer contained in the received response in saidsecond storage means.
 15. A mobile computer according to claim 6 ,wherein the binding information includes a registered time and aneffective period, and said mobile computer further comprises means forerasing the binding information which has expired.
 16. A positionidentifier management method comprising: storing by a mobile computerlatest binding information including a compatible node identifier and acompatible position identifier in storage means of said mobile computerwhen the movement of said mobile computer is detected, the compatiblenode identifier containing a first virtual network identifier assignedto said mobile computer which moves between networks and a nodeidentifier for uniquely specifying said mobile network, the compatibleposition identifier containing a second network identifier which isusable only by mobile computers assigned to a network to which saidmobile computer is moved and the node identifier; specifying by saidmobile computer at least one position identifier management apparatuswhich manages said mobile computer from position identifier managementapparatuses, disposed on a network, for storing the binding informationwhich is requested to be registered from an external mobile computermanaged by said position identifier management apparatuses, and forresponding to a query about the binding information; sending aregistration request to register the latest binding information aboutsaid mobile computer from said mobile computer to one of the specifiedposition identifier management apparatuses; storing the bindinginformation contained in the registration request in said storage meansof the position identifier management apparatus which has received theregistration request after the position identifier management apparatusdetects that the sender of the registration request is said mobilecomputer and authenticates said mobile computer as a valid mobilecomputer; and sending the registration request to an external positionidentifier management apparatus which also manages said mobile computerafter said mobile computer which has sent the registration request isauthenticated as a valid mobile computer.
 17. A position identifiermanagement method according to claim 16 , wherein said mobile computersends a query containing the position node identifier of said mobilecomputer to a server for storing a relationship between the compatiblenode identifier and an address of a position identifier managementapparatus which manages said mobile computer provided with thecompatible node identifier, and receives a response to the query fromsaid server, thereby specifying the position identifier managementapparatus which manages said mobile computer.
 18. A position identifierprocessing method for a mobile computer, comprising the steps of:storing binding information including a compatible node identifier and acompatible position identifier in storage means of said mobile computer,the compatible node identifier containing a first virtual networkidentifier assigned to said mobile computer which moves between networksand a node identifier for uniquely specifying said mobile computer, thecompatible position identifier containing a second network identifierwhich is usable only by mobile computers assigned to a network to whichsaid mobile computer is connected and the node identifier; acquiring,when a destination address of a packet to be transmitted is designatedwith the compatible node identifier and when said storage means does notstore the compatible node identifier, the binding information containingthe compatible node identifier by making a query to a positionidentifier management apparatus which manages the binding informationconcerning a mobile computer provided with the compatible nodeidentifier; and converting the compatible node identifier representingthe destination address of the packet to be transmitted into theacquired compatible position identifier, and setting the compatibleposition identifier of said mobile computer stored in said storage meansas the source address of the packet.
 19. A position identifierprocessing method according to claim 18 , wherein, when an error messageindicating that the packet has not reached is returned after sending thepacket having the compatible position identifiers as the source addressand the destination address, a query is made to the position identifiermanagement apparatus which manages the binding information concerningthe mobile node provided with the compatible node identifiercorresponding to the compatible position identifier so as to acquire thelatest binding information concerning the mobile computer provided withthe compatible node identifier, and then, the packet is re-transmitted.20. A position identifier processing method for a mobile computer,comprising the steps of: storing binding information including acompatible node identifier and a compatible position identifier instorage means of said mobile computer, the compatible node identifiercontaining a first virtual network identifier assigned to said mobilecomputer which moves between networks and a node identifier for uniquelyspecifying said mobile computer, the compatible position identifiercontaining a second network identifier which is usable only by mobilecomputers assigned to a network to which said mobile computer isconnected and the node identifier; and converting, when each of a sourceaddress and a destination address of a received packet is designatedwith the compatible position identifier, the compatible positionidentifier into the compatible node identifier by at least substitutingthe second network identifier of the compatible position identifierwhich designates the source address of the packet by the first networkidentifier, and also verifying the integrity of the compatible nodeidentifier which designates the source address of the packet.
 21. Aposition identifier management apparatus for supporting the movement ofa mobile computer between networks, comprising: storage unit configuredto store binding information concerning said mobile computer managed bysaid position identifier management apparatus, said binding informationincluding a compatible node identifier for uniquely specifying saidmobile computer and a compatible position identifier for uniquelyspecifying a position of said mobile computer on a network; registrationunit configured to register the binding information in said storage unitin response to a registration request to register the bindinginformation from another apparatus; and transmitting unit configured totransmit the binding information in response to a query about thebinding information concerning said mobile computer from anotherapparatus when said binding information is stored in said storage unit.22. A mobile computer which moves between networks, comprising: firststorage unit configured to store binding information including acompatible node identifier and a compatible position identifier, thecompatible node identifier including a first virtual network identifierassigned to said mobile computer which moves between networks and a nodefor uniquely specifying said mobile computer, the compatible positionidentifier including a second network identifier which is usable only bymobile computers assigned to a network to which said mobile computer isconnected and the node identifier; second storage unit configured tostore binding information concerning at least one of external mobilecomputers with which said mobile computer is to communicate, saidbinding information including a compatible node identifier and acompatible position identifier, the compatible node identifier includinga first virtual network identifier assigned to said external mobilecomputer which moves between networks and a node identifier of saidexternal mobile computer, the compatible position identifier including asecond network identifier which is usable only by mobile computersassigned to a network to which said external mobile computer isconnected and the node identifier of said external mobile computer;determining unit configured to determine whether the binding informationis to be used for a packet transmitting or receiving operation; andconversion unit configured to perform, when said determining unitdetermines that the binding information is to be used, a conversionoperation by converting the compatible node identifier to the compatibleposition identifier when the packet is to be transmitted and byconverting from the compatible position identifier to the compatiblenode identifier when the packet is to be received.